This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. With the growing acceptance of cygwin and other public-domain packages such as python and perl/tk as a versatile and extendable programming environment for the windows operating system, we have undertaken a port of some of our most commonly used simulation and non-linear least-squares (NLLS) fitting routines to the windows OS. We have done so in order to facilitate their dissemination amongst the ESR community, many of whom use the windows OS. This is particularly important for the NLLS fitting routines with graphical display of the spectrum and fit that we use with our 1D spectra. The original package was written for the X-windows system and the unix operating system. In order to facilitate the graphics calls within windows, we have largely completed a rewrite of the graphics intensive parts of the code using perl/tk. The user interface is also being rewritten in python as experience has shown that this interpreted language offers significant advantages for testing and debugging. From the user[unreadable]s perspective, the entire package consisting of the source code and makefile will compile and run "out of the box" without additional effort by the researcher, once the public domain cygwin, perl/tk and python packages are installed. In order to facilitate the dissemination of these new software packages, we will place them on the center's ftp site, accessible through our homepage, when the package is stable enough for extensive dissemination. We are also in the process of incorporating suggestions for improvements in the software package based on feedback from users in the ESR community. As time and resources permit, we will port these simulation and fitting packages to the macintosh OS.